Changing the Background of an MDI Parent Form

[jmcilhinney]

C# version here.

I've posted a solution to this question many times already and it's come up again recently, so I figured a little CodeBank submission might be helpful. First, some background information:

When you set the IsMdiContainer property of a form to True, the IDE adds an MdiClient control to your form. The grey background you see is not the form but the MdiClient control. If you set the BackColor or BackgroundImage properties of the form it will have no effect because you can't see the form's background.

Now, it is actually this MdiClient control, not the form itself, that hosts the MDI child forms. If you add any controls to the parent form then they will either be behind the MdiClient and, therefore, not visible or else on top of the MdiClient and, therefore, on top of the MDI child forms too.

The developer is not intended to mess with this MdiClient control so no member variable is provided with which to access it. It's not inaccessible though, so if you want to change the visible background of the parent form you can do this:

Private Sub Form1_Load(ByVal sender As Object, _
                       ByVal e As EventArgs) Handles MyBase.Load
    For Each ctl As Control In Me.Controls
        If TypeOf ctl Is MdiClient Then
            'Set properties of ctl here, e.g.
            ctl.BackgroundImage = My.Resources.MdiBackgroundImage
            Exit For
        End If
    Next ctl
End Sub

[kuldevbhasin]

I've posted a solution to this question many times already and it's come up again recently, so I figured a little CodeBank submission might be helpful. First, some background information:

When you set the IsMdiContainer property of a form to True, the IDE adds an MdiClient control to your form. The grey background you see is not the form but the MdiClient control. If you set the BackColor or BackgroundImage properties of the form it will have no effect because you can't see the form's background.

Now, it is actually this MdiClient control, not the form itself, that hosts the MDI child forms. If you add any controls to the parent form then they will either be behind the MdiClient and, therefore, not visible or else on top of the MdiClient and, therefore, on top of the MDI child forms too.

The developer is not intended to mess with this MdiClient control so no member variable is provided with which to access it. It's not inaccessible though, so if you want to change the visible background of the parent form you can do this:

Private Sub Form1_Load(ByVal sender As Object, _
                       ByVal e As EventArgs) Handles MyBase.Load
    For Each ctl As Control In Me.Controls
        If TypeOf ctl Is MdiClient Then
            'Set properties of ctl here, e.g.
            ctl.BackgroundImage = My.Resources.MdiBackgroundImage
            Exit For
        End If
    Next ctl
End Sub

i tried the code and am using vb.net 2003 it gives a blue line on

my

says :

Name "My" is not declared

if i use Me instead of My it says "Resources" is not a member of the form
what can i use instead of it?
thankx...

[jmcilhinney]

i tried the code and am using vb.net 2003 it gives a blue line on

my

says :

Name "My" is not declared

if i use Me instead of My it says "Resources" is not a member of the form
what can i use instead of it?
thankx...

That part of the code is not really relevant to the topic of this thread. That is simply getting an Image object form the application resources. You can get your Image object in whatever way is appropriate. You can get it from a file or, if you have embedded it as a resource, you can get it in the standard way for retrieving resource images in .NET 1.x. That is beyond the scope of this thread so I'm not going to explain it here. I suggest that you search MSDN as there's example code available. If you still aren't sure then post on the VB.NET forum.

[jmcilhinney]

Here's some more succinct code that uses extension methods and, therefore, requires .NET 3.5 or later:

Private Sub Form1_Load(ByVal sender As Object, _
                       ByVal e As EventArgs) Handles MyBase.Load
    'Get a reference to the one and only MdiClient in the Controls collection.
    With Me.Controls.OfType(Of MdiClient).Single()
        'Set properties of the MdiClient here, e.g.
        .BackgroundImage = My.Resources.MdiBackgroundImage
    End With
End Sub